This invention relates to the art of detecting leaks in packages, and more particularly to a method and apparatus for automatically determining whether a package falls within acceptable leakage parameters.
Most perishable goods are packaged in some form of sealed container to provide acceptable shelf life. Some means for testing package integrity must be included in the manufacturing process to insure product quality.
Package integrity is particularly important to the cigarette industry. After cigarettes are assembled into a pack--generally, either a soft paper package or cardboard box, both having a foil inner liner--the pack is sealed within a moisture-proof polypropylene wrapper. Moisture loss is the single most important determinant in shelf life, so it is important that manufacturers be able to determine whether the polypropylene wrapper is completely sealed. Lacking the ability to make rapid and accurate package integrity determinations, manufacturers must choose between an overly conservative product rotation policy or the possibility of consumer dissatisfaction with cigarettes which have become "stale" through moisture loss.
The generally accepted method for testing package integrity falls far short of the goals of reliability or rapidity. Primary reliance is placed upon visual inspection; given that the overwrap is transparent and that the production line is moving rapidly, the hazards of relying entirely upon visual inspection are glaringly obvious. The present method of physically testing package integrity is both cumbersome and potentially hazardous. The test instrument consists of a mercury bath with a wire mesh fixture in the shape of a cigarette pack, protruding above the bath. A vacuum line is located within the fixture, above the surface of the mercury. The pack to be tested is carefully slit in half and the polypropylene wrapper removed. The wrapper is then placed over the wire mesh fixture such that its open end extends into the mercury bath. The chamber thus defined by the wrapper and the mercury surface is then evacuated via the vacuum line, and the ability of the wrapper to sustain a selected vacuum level is measured. Plainly, this method is both slow and labor-intensive. Additionally, it is inherently incapable of providing rapid information feedback, as the potential hazard in locating an open mercury bath within a production area is amply documented. Clearly, the cigarette industry needs a rapid and reliable means for testing package integrity.
The package testing art does not offer a suitable alternative to the present method. For example, U.S. Pat. No. 4,118,972, to Goeppner, discloses a device which requires that the package be evacuated and then surrounded by an inert gas, such as helium. Apparatus connected to the evacuation means then detects the amount of the gas penetrating into the package as an indication of the leakage rate. Another system, seen in Westervelt, U.S. Pat. No. 3,872,712, relies upon the timed application of compressed air, at several pressure levels, in conjunction with somewhat elaborate control and measurement apparatus, to measure leakage.
The complexity of such devices has led manufacturers of mass-produced consumer goods to abandon the idea of direct, on-line, measurement of package leakage. Rather, these manufacturers usually rely upon indirect methods, such as visual inspection of the package seal, or off-line methods, like the inert gas atmosphere system described above.